This research is directed towards understanding the mechanism of estrogen action in normal and abnormal uterine growth. The growth and development of the uterus is regulated by the interaction of estrogens with a specific estrogen receptor. The molecular mechanism of the estrogen-mediated activation of the receptor is investigated in human, rat and calf uteri. The estrogen receptor from calf uteri is being purified. The interactions of 3H estradiol and its receptor are investigated by gel chromatography and sucrose gradient centrifugation analysis. The molecular bases for the activation of the estrogen receptor will be described.